Popular Science Monthly/Volume 10/November 1876/The Moon's Influence on the Weather
By Professor M. A. F. PRESTEL.
A SUDDEN and considerable fall of the barometer is of frequent occurrence; but to find a case identical with that of November 22, 1873, I had to search my journals for many years back. It is worthy of note that, in 1854, an equally sudden and considerable fall of the barometer took place here on the coast of the North Sea on precisely the same days as in 1873. According to observations made at Emden, the barometric column on November 21, 1873, at 6 a. m., was 762.3 millimetres, and it then fell steadily till 2 p. m. on the 22d, when it reached the minimum, 732.5 millimetres, and then it again began to rise. At 6 a. m. of November 21, 1854, the barometer stood 760.7 millimetres, and the mercurial column then steadily fell until 6 a. m., November 23d, when it was 734.7 millimetres; it then began to rise. The point to which I would call special attention is that, on the occasion of both of these great falls of the barometer, the position of the moon with respect to the earth was precisely the same. There was new moon at 3 a. m. of November 20, 1873, and at 8 a. m. of November 20, 1854; in 1873 the moon entered the southern lunistice at 3 a. m. on November 23d, and in 1854 at 6 a. m. of November 23d; in both years the moon's declination on November 23d was 27° south.
Still, the occurrence of storms and barometric minima over North-western Europe on November 22, 1873 and 1854, at the period of the lunistitia and of the new moon, might be merely accidental; but that it was not accidental is shown by sundry mutually corresponding phenomena in the atmosphere, which were observed during these two years. During the month of October, 1873, the average height of the barometric column was 757.1 millimetres, and for the same month in 1854 it was 757.2 millimetres; the barometric mean for the five days between the 22d and the 28th was, in 1873, 750.7 millimetres, and in 1854, 748.7 millimetres; the minimum was reached, in 1873, on October 23d, and in 1854 on October 25th, being in the former case 734.9 millimetres, and in the latter, 734.5 millimetres. In 1873 the maximum was reached in the evening of October 28th—773.7 millimetres, and in 1854 at noon of the 28th—774.9 millimetres. The weather was also the same in both years from the 3d to the 7th, and from the 21st to the 27th of October. From the 5th to the 7th there were frequent and heavy falls of rain; on the 7th, in 1873, and on the 5th, in 1854, there were violent thunder-storms. On both years from the 21st to the 25th the atmosphere was in a state of violent disturbance, the barometric column being very low. And here we may state that there was new moon at 11 a. m. on October 21, 1873, and at 9 p. m. on October 21, 1854; that in 1873 the southern lunistice occurred at 10 p. m. of the 26th, and in 1854 at 9 p. m. of the 26th; and that the moon's declination at the time was about 27° south.
Further, from the 13th to the 16th of November, 1873, the distribution of atmospheric pressure over Europe and the state of the weather were similar to what they were on the same days in 1854. The fearful ravages wrought by the storms in the Black Sea on the days between the 13th and the 16th of November,1854 (the Crimean War being then in progress), will render those days ever memorable. The numerous shipwrecks in the sea of Azof, and the loss of English and French war-ships in the Black Sea on the 13th and 14th, showed how desirable and necessary a thing it was that there should be found some means of warning seafarers of the approach of storms. It was these disasters which gave occasion to the establishment of storm-signals. From the 13th to the 15th of November, 1873, after a period of calm, with high barometer over the greater part of Northwestern Europe, we find succeeding a similar barometric minimum, and a storm area advancing across the Mediterranean toward the Black Sea.
At any given point of the earth's surface the state of the weather always depends on the prevailing air-currents. The annual and the secular periodic changes of the oceanic and the atmospheric currents are repeated in the weather-changes. And on the phenomena which, however imperfectly, establish this periodicity, is based the universal belief that the moon has an influence on the weather. The researches and calculations which have been made by meteorologists to determine the periodicity of weather phenomena, and the influence of the moon upon the latter, have hitherto been fruitless, and this simply because the observations of single stations only have been taken into account. From observations made at one point it is impossible to obtain decisive results as to secular periodic weather-changes, even though these observations were to be carried on for a hundred years or more. The terrestrial atmospheric currents, in their passage over the same portion of the earth's surface (whether this passage be periodic or not periodic), never take the same route, or have the same limits, and consequently the localities over which they pass on their return will happen to be at one time in the centre of the current, at another time more or less near to its northern or its southern edge.
Under these circumstances the state of barometer and of thermometer, the amount of precipitation, the force of the wind, etc., upon which these researches are based, must yield conflicting results. Some, however, have supposed that-better results might be obtained by combining these quantities, and taking the mean of all the readings. This method quite does away with anomalies, it is true, but then the result has no specific value whatever, though the aim of all such researches must always be to determine the weather specifically. The periodicity of weather phenomena can only be determined by means of investigations carried on according to the geographical method, i. e., by studying these atmospheric phenomena in their continuity both as regards time and space.
As has been already said, the track of the storm of November l7th-23d layover nearly the same regions of the northern hemisphere in 1873 and 1854. Had these air-currents taken a course only a few degrees more to the north or to the south, their existence and their identity would have been so ill determined by the barometer of a single locality that they might easily have been overlooked.
On the 28th of November, 1873, at 10 p. m., the barometer at Emden stood at 756.4 millimetres, and then kept on falling till the 30th, at 8 a. m., when it was 744.2 millimetres; after this it rose till at 10 p. m. it was 762.6 millimetres. This not very considerable fall of the barometer would not have deserved special notice, were it not followed on the evening of the 29th by a storm of some violence, which through the night became a hurricane. In 1854, at the same period of the year, the barometer underwent a similar change, only much greater. On November 27th, at 10 p. m., the height of the barometric column was 757 millimetres. It then fell, till on the 29th, at 2 p. m., it was 727.8 millimetres, when it began rising till it reached 757.9 millimetres at 8 a. m., on the 30th. The quantitative difference of barometric pressure at Emden on November 27th and 28th, between the years 1873 and 1854, is simply the result of the difference in the tracks of the storms, and the consequent distance of the place of observation from the storm-centre. At Thorshavn, between November 25th and 28th, in 1873, the barometric changes were precisely the same as had been observed at Emden on the same days in 1854. In 1873, at 9 p. m. of the 25th, the mercurial column at Thorshavn was 757.3 millimetres; on the 26th, at 8 a. m., it was 746.9 millimetres; on the 26th at 9 p. m., 729.2 millimetres; on the 27th, at 8 a. m., 729.8 millimetres; on the 28th, at 8 a. m., 747.3 millimetres.
With the moon in a like position with respect to the earth, there occurred, December 15-18, 1873 and 1854, just as on the 21st and 22d of November, a sudden and great fall of the barometer, accompanied by a fearful storm. In 1873, on the evening of the 13th, and in 1854, on the morning of the 14th, the moon was in the descending node.. The moon's declination in 1873, at 3 p. m. of the 15th, and in 1854 at 7 a. m. of the 16th, was 12° south. At Emden, in 1873, the barometer fell on the 15th and 16th, from 768 to 745 millimetres, or 23 millimetres. At Skudesnäs the fall on the 15th and 16th December amounted to 25 millimetres; at Stockholm, on the 16th, to 20 millimetres; at St. Petersburg, from the 15th to the 17th, to 30 millimetres. The track of the centre of this storm entirely agrees with that of the storm of November 14th-22d. At 1 a. m. of December 14th, we find at Washington, North Carolina, a barometric minimum of 744.2 millimetres, and by 7h. 35m. this had advanced as far as Halifax. Here, at the time specified, the barometer had fallen to 735 millimetres. On the 14th, at 4h. 35m., the barometric minimum had passed in a northeast direction over Newfoundland, crossing the Atlantic Ocean. At Thorshavn, where, on the 14th, at 8 a. m., the barometer had stood at 757.4 millimetres, it had on the morning of the 16th fallen to 731.9. At Aberdeen, the barometer on the morning of the 16th stood at 735 millimetres.
In 1854, on the morning of December 17th, the barometer at Emden showed 752.2 millimetres; it then fell till noon on the 18th, when it was 731.1 millimetres, and then began to rise again. At the beginning of the fall of the barometer, a storm from the southwest set in, which increased in force till it became a hurricane. The rain which fell during the storm amounted to 18.9 millimetres.
At Cologne, at 3h. 41m., December 18, 1854, the barometer showed 726.6 millimetres—a barometric minimum never before observed there since 1830.
In 1854 the track of the storm-centre traversed Northern France and Germany: thus, as on November 22d,it was more southerly than in 1873.
Such concordant atmospheric phenomena as these, when the moon occupies the same position relating to the earth, might be quoted at great length. The moon, as it governs ebb and flow, so too determines oceanic currents, and, by means of these, atmospheric currents. From this it follows that the influence of the moon upon that portion of the atmosphere which overlies the continents must be less than that upon the supra-oceanic atmosphere.—Gaea.